Activation of Thoeris antiviral system via SIR2 effector filament assembly. (https://pubmed.ncbi.nlm.nih.gov/38383786/)

These scientists were studying how bacteria defend themselves against viruses called bacteriophages. They found that some bacteria have a defense system called the Thoeris system, which has two parts: a sensor that recognizes when the virus is attacking, and an effector that stops the virus from replicating by destroying important parts of the cell.

The scientists discovered that a protein called ThsB acts as the sensor in the Thoeris system. ThsB makes a special molecule called 1''-3' glycocyclic ADP ribose (gcADPR) when it detects the virus. This gcADPR then binds to another protein called ThsA, which is the effector part of the system. When gcADPR binds to ThsA, it triggers a series of changes in the protein that allow it to start destroying a key cell metabolite called NAD(+).

Using a special microscope called cryogenic electron microscopy, the scientists were able to see the structure of ThsA when it was activated by gcADPR. They found that gcADPR causes ThsA to form long filaments, which help stabilize the active form of the protein and allow it to rapidly deplete NAD(+). This process acts like a switch that turns on ThsA's ability to fight off the virus.

Tamulaitiene G., Sabonis D., Sasnauskas G., Ruksenaite A., Silanskas A., Avraham C., Ofir G., Sorek R., Zaremba M., Siksnys V. Activation of Thoeris antiviral system via SIR2 effector filament assembly. Nature. 2024 Feb 21. doi: 10.1038/s41586-024-07092-x.